As known from the U.S. PCT Publications WO87/07565 and WO88/06983, the piston of a shock absorber comprises the main valve embodied in the body of the piston and a pilot control chamber accommodated in it, which acts upon the valve plate of the main valve. The pressure of the pilot control chamber acts upon the valve plate via a relief piston, which is sealed off from the body by means of a gap seal, to avoid seizing at the inside circumference as well as on the outside circumference of its annular shape, and is acted upon by an additional compression spring. The opening existing in the relief piston from the pilot control chamber to the adjoining work chamber is reduced by means of a shim, placed on the inside, with an incorporated relatively small throttle restriction, and this shim in turn is pressed by another spring against the relief piston and that spring is retained in position in turn by a special guide element.
Because of the great number of individual moving parts, seizing can easily occur, and moreover the production of these individual parts is overall very expensive, especially since work must be done with relatively close tolerances because of the use of gap seals, so that as a rule only metal-cutting production methods, rather than deforming production methods, can be employed in manufacture.
The valve plate is guided with its inside diameter on the outside diameter of the neck joining the body of the piston to the piston rod and is acted upon by compression springs by means of a pressure plate. Because the spring forces do not always act centrally, it is possible that the valve plate may tilt unilaterally upward, unevenly--especially when the spring force is exerted upon a small diameter. Previously, no stroke limitation was provided.
In the interior of the neck, a pilot control valve is typically formed, which varies the pressure in the pilot control chambers of the main valve To that end, the neck is embodied as hollow on the inside, and in it, a slide sheath is first displaceable, resting tightly in the axial direction and traveling in it in turn is the actual slide, acting as a pressure balance; in the region of the radially communicating openings with the pilot control chambers, the actual slide has an annular groove, with the aid of which, given a suitable position, communication can be established between the two pilot control chambers.
On its other face end, this slide ends with an unaltered diameter at the face end of a likewise longitudinally hollow sheath, which is retained spaced apart from an electromagnet by a spring on the opposite end. This sheath has grooves on its outside circumference that communicate with the central bore and that effect sealing between the sheath and the slide sheath only by means of the face end toward the slide. When the electromagnet attracts, the sheath is displaced counter to the force of the spring and opens this seal, resulting in a relative shifting of the slide sheath and the slide and thus varying the free cross section of the communication between the pilot control chambers. The individual parts of this pilot control valve must be made with very close tolerances.
The neck is thrust into the end of the piston rod, where it is secured by a wave nut that simultaneously acts as a stop for one of the two compression springs of the main valve.